The invention relates to interposer assemblies used for forming electrical connections between spaced contact pads on circuit members.
Interposer assemblies form electrical connections between densely spaced contact pads on adjacent parallel circuit members. Interposer assemblies are used wherever dense connections are required. The assemblies are particularly well suited for use in electronic devices such as cellular telephones, computers, radios, control circuits and the like. The assemblies enable a reduction in the size and weight of the electronic devices.
The contact pads on the two circuit members are typically arranged in identical patterns. The interposer assembly includes an insulating plate and a plurality of through-contacts carried in the plate and arranged in the same pattern as the pads on the circuit members. Commonly, the circuit members are a circuit board and a ceramic plate carrying integrated circuits. The interposer assembly is sandwiched between the circuit board and the ceramic plate with the contact pads against the top and bottom surfaces of the plate. The contact pads press against the through-contacts, forming electric connections between aligned pairs of pads.
The contact pads must make reliable, low resistance electrical connections with the through-contacts. The contact pads are conventionally made from a nickel or copper alloy substrate with a thin protective plating. The plating may be thin and allow corrosion of the underlying contact pad. Corrosion products accumulate on the outer surfaces of the contact pads and increase the contact resistance between the pads and the through-contacts.
The protective plating may be a film of corrosion-resistant metal such as gold, silver or platinum. The film is typically 3 to 8 millionths of an inch thick. The plating covers the metal substrate and protects the substrate from corrosion. The plating metal is also an excellent conductor of electricity and reduces contact resistance.
The thin plating film will often contain minute defects such as pores and pinholes. In these areas the film thickness is very thin and the substrate metal is vulnerable to corrosion. The thickness of the plating film must be sufficient to protect the metal substrate from corrosion despite the film defects. However, providing a thick film is wasteful and expensive.
Electronic devices are often used in corrosive environments such as hot, humid air. The air often carries contaminants, such as chlorides from sea spray or sulfides found in air pollution. The contact pads are exposed to the airborne contaminants. The chlorides or sulfides in the air attack plating defects and can corrode the contact pads.
Thus, there is a need for an improved interposer assembly which protects plated pads from corrosive environments and permits use of thin film plating on pads. The interposer assembly should be compatible with existing circuit designs.
The invention is improved interposer assembly having a sealing member that surrounds the plate when the interposer assembly is sandwiched between the circuit members. The sealing member is also sandwiched between circuit members and seals the interior of the gasket. The sealing member prevents airborne contaminants from entering the spaces between the plate and circuit members and corroding contact pads.
In a preferred embodiment of the invention, the sealing member is a resilient circumferential gasket. The gasket surrounds the interposer plate and includes circumferential top and bottom sealing portions that extend beyond the top and bottom sides of the plate. When the interposer assembly is sandwiched between the circuit members, the gasket is compressed between them. The gasket sealing portions abut the circuit members and seal the interior of the assembly against contaminants.
The plate includes mounting ears that extend away from the plate and support the plate on a frame. The ears extend through slots in the gasket and hold the gasket on the plate. The plate and gasket can be fastened to the frame to form a connection subassembly which is later sandwiched between the circuit members.
The improved interposer assembly of the present invention can be incorporated into existing interposer assemblies. The assemblies can be used in corrosive environments to prevent exposure of contact pads to contaminants. The contact pads do not need to be heavily plated. Thin plating films may be used, with resultant cost savings.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are five sheets of drawings and one embodiment.